1. Field of the Invention
The present invention relates to an external cylinder and a silencer provided with the external cylinder and specifically relates to a silencer whose external cylinder is formed from a resin material.
2. Description of the Related Art
Heretofore, a silencer is provided with an external cylinder, an internal cylinder arranged inside the external cylinder, and an acoustic absorbent filled between the internal cylinder and the external cylinder. Then, a cap with an exhaust port is detachably provided in one end of the silencer, while an exhaust pipe is allowed to detachably communicate with the other end thereof.
Further, a silencer whose external cylinder is formed from, e.g., carbon fiber reinforced plastics to reduce the weight is being used in auto racing or the like. An acoustic absorbent thus filled deteriorates and decreases with the use thereof and hence it is necessary that the cap and the exhaust pipe are detached to refill another acoustic absorbent therein as need arises.
However, there has been a problem that when a high-temperature exhaust gas contacts with an inner surface of the external cylinder formed from the carbon fiber reinforced plastics, the plastics spatters to damage the external cylinder. To solve this problem, a certain silencer is disclosed in e.g., Japanese patent publication No. 2885348, in which a metallic layer is provided on the inner surface of the external cylinder to prevent the exhaust gas from contacting with the inner surface, thereby restraining the damage of the external cylinder. Nevertheless, there still remains a problem that in refilling the acoustic absorbent, the cap and the exhaust pipe contact with the metallic layer formed on the inner surface of the external cylinder when detaching or attaching the cap and the exhaust pipe, and thus the metallic layer is damaged as it is exfoliated, for example.